Patterning method

ABSTRACT

A method for patterning a device layer, for example of an organic electronic or optoelectronic device, using a patterned stamp. The method comprising the steps of (a) providing a substrate, (b) bringing the patterned stamp into contact with the substrate, (c) removing the patterned stamp from the substrate, characterized in that step (b) is carried out so that the surface energy of the substrate is modified in accordance with the pattern, and that the method further comprises a step (d) depositing a solution of a device layer on the substrate after the patterned stamp has been removed, whereby the surface energy of the substrate determines the deposition pattern of the device layer.

The present invention relates to a method for patterning a device layerand to devices made using the method. The invention is particularlyconcerned with a method for patterning an optoelectronic device layerthat is simpler and more cost effective than previously known methods.

One class of optoelectronic device that is of particular interest of thepresent invention is an organic light-emitting device (OLED). Thesedevices employ an organic material for emission.

Polymers are an attractive choice for use in OLED devices. For example,WO 90/13148 describes such a device comprising a semiconductor layercomprising a polymer film that comprises at least one conjugated polymersituated between electrodes. Other polymer layers capable oftransporting holes or transporting electrons to the emissive layer maybe incorporated into such devices.

In a typical OLED device, the anode electrode typically is a layer oftransparent indium-tin oxide (ITO). The ITO typically is covered with atleast a layer of a thin film of an electroluminescent organic material.A hole transport layer may be provided between the ITO and the organicmaterial. A final layer forming a cathode electrode, which is typicallya metal or metal alloy covers the organic material.

In order to fabricate the device structure, various techniques forfabricating nano structures have been developed. To obtain functionaldevices it often is necessary to pattern the active device layers andthe electrodes.

Organic light emitting devices (OLED's) which make use of thin films ofpolymer are becoming an increasingly popular technology for applicationsin devices comprising a plurality of OLED pixels arranged to form adisplay, such as a flat panel display (FPD). Such an OLED including apixel arrangement typically comprises a plurality of luminescent pixelsthat are arranged in a matrix form.

To form an array of OLED's, constituent materials must be patterned. Apixelated OLED device includes, for example, a plurality of firstelectrode strips formed on a substrate. The strips are arranged in afirst direction. One or more organic layers are formed on the firstelectrode strips. A plurality of second electrode strips is formed overthe organic layers in a second direction that typically is orthogonal tothe first direction. The intersections of the first and second electrodestrips form pixels.

Patterning active device layers and electrodes previously has been doneusing standard photolithography processing.

Standard photolithography processing typically involvesphotolithographic and etching techniques. Photolithographic techniquesall share the following operational principal;

exposure of an appropriate material to electromagnetic radiation inorder to introduce a latent image into the material as a result of a setof chemical changes in its molecular structure;

subsequent developing of the latent image into relief structures throughchemical etching.

Patterning of the latent image can be achieved by interposing a maskbetween the source of radiation and the material. When masks are used,the lithographic process yields on the material a replica of the patternon the mask.

This method commonly has been used to produce a patterned anode on asubstrate, for example ITO tracks on a glass substrate. For example, aphotosensitive resist layer is deposited as a layer on an anode layer.The resist layer is exposed with radiation having the desired patterndefined by a mask. After development, unwanted resist is removed toexpose portions of the anode beneath. The exposed portions are removedby a wet etch, leaving the desired pattern on the anode layer. Cathodestrips may be created similarly. It can be seen that this conventionaltechnique requires numerous steps, increasing raw process time andmanufacturing costs.

Several problems have arisen in the chemical etching of some materialsand the chemical compatibility of some materials with conventionalphotoresists. Particularly, standard photolithography processing is notsuitable for some polymers because the surface could be exposed tosolvents or UV light, which might cause material degradation. Thus, ithas been considered that there is a need to develop special patterningtechniques for polymers. It therefore has been considered desirable topattern conducting electrodes and semiconducting polymers in deviceswith non-photolithographic techniques.

One alternative to photolithography is soft lithography. This is thecollective name for a set of lithographic techniques using a patternedelastomer stamp to generate or transfer the pattern. Soft lithographypatterning techniques are based on physical contact, not the projectionof light through a mask, as in photolithography. Soft lithography offersimmediate advantages over photolithography for applications in whichpatterning non-planar substrates, unusual materials, or large areapatterning are the major concerns. As described in Advanced Materials2000, 12 No. 4 page 269 to 273, there are several advantages of usingsoft lithography compared to conventional photolithography: it is lesscostly, has no optical diffraction limit, allows control of thechemistry of a patterned surfaced, does not expose the sample tohigh-energy radiation and can easily be applied to non-planar surfaces.Soft lithography is a gentle process that therefore is of great interestfor patterning sensitive materials such as polymers.

Soft lithography includes microcontact printing (μCP); replica moulding,self assembled monolayers; put-down and lift-up; and micromoulding incapillaries (MIMIC) techniques.

A replica moulding (soft embossing) technique is summarised in FIG. 1 ofAdvanced Material 2000, 12 No. 3 page 189 to 195. A patterned elastomeris put in conformal contact with an active polymeric film area and theassembly is brought to the polymer softness transition temperature.After cooling, the patterned elastomer stamp is removed and leaves thegrating pattern on the polymer surface. This technique also is generallydescribed in FIG. 3(A) of Chemical Reviews 1999, Vol. 99 No. 7 page 1823to 1848.

Three different general methods of soft lithography are summarised inFIG. 1 on page 270 of Advanced Materials 200, 12 No. 4. It can be seenthat, in general, microcontact printing and lift-up both involve atransfer of polymer material either from the rubber stamp to thesubstrate or from the substrate to the rubber stamp. The MIMIC techniquenecessitates introducing polymer material into capillaries that areformed when the stamp is in conformal contact with the substrate.

The specific disclosure of this document is limited to microcontactprinting of PEDOT-PSS onto ITO substrate; microcontact printing ofPEDOT-PSS onto gold substrate; lift-up of PEDOT-PSS on glass substrateand micromoulding in capillaries of polyurethane. The MIMIC method wasused to pattern the thermally evaporated aluminium cathode and the othertwo methods patterned the anode. Electrically separated anode lines wereachieved by putting PEDOT-PSS onto gold and, through wet etching,removing the gold between the PEDOT-PSS lines.

WO 01/04938 provides an alternative to conventional photolithographicand etching techniques. The method is a stamping or embossing method anduses a stamp made of a hard material such as steel, silicon, or ceramic.A pattern is defined by protrusions on the surface of the stamp. A loadis applied on the stamp forcing the stamp against the substrate.

This causes the pattern on the stamp to be transferred to the substrate.

A specific lift-up technique is described in WO 01/39288. This documentrelates to patterning an electrode layer using a silicon stamp. Thepatterned stamp is coated with an adhesive material such as a metal. Thepatterned stamp is removed such that the portions of the electrode layerin contact with the raised portions of the stamp are removed with thestamp.

As acknowledged in WO 00/70406, the stamp material used in many softlithography techniques is problematic when used in combination withpolymers solvated in some organic solvents such as isopropanol, xylene,chloroform or water. Isopropanol, xylene and chloroform prevent thepatterning of many polymers because these solvents can swell the stampand destroy the fine pattern to be transferred. Alternatively, thepatterning of water-soluble polymers prohibits the use of some softlithography techniques such as MIMIC as water is not easily transportedthrough the extremely non-polar elastomeric stamp.

In order to address this problem, WO 00/70406 provides a method forpatterning a polymer film that involves depositing onto a materialsurface a thin film of polymer, applying to the material surface a stampmade of an elastomeric material in conformal contact with the surface ofthe thin film. Portions of the thin film contact one or more protrudingelements of the elastomeric stamp and are attached to the protrudingelement. These portions are removed from the material surface with thestamp. In the method, no solvent is used. The method can be consideredto be a “lift-up” soft lithography method. An equivalent “put-down”method to the “lift-up” method also is described in this document.

An alternative method is to combine soft lithography with theself-assembled monolayer technique. A hydrophilic monolayer patternresiding on a hydrophobic background, or a hydrophobic monolayer patternresiding on a hydrophilic background, will direct polymer solutions onthe surface to selectively wet and spread on one of these regions, andfinally a duplicated polymer pattern forms after solvent evaporation.This method can be controlled by the liquid and solid surface freeenergy. However, the method requires suitable monolayer material beingtransferred to a patterned area, which is probably unwanted in the finalstructure. The chemical step involved in the transfer of theself-assembled monolayer also influences the final properties of thepatterned film.

In parallel with the above mentioned soft lithography techniques forfabricating patterned nano structures, in recent years, technology hasbeen under development for obtaining functional devices by formingprescribed patterns by applying thin films having different propertiesonto different zones on the same substrate. However, a problem arises atthe process surface in that the different thin film materials becomemixed on the substrate. This is because the liquid material that isdischarged into one zone on the substrate flows over into adjacentzones. What is commonly done to overcome problems such as this is toprovide protruding portioning members (called “banks” or “rises”) topartition off different thin film zones and then to fill the areasenclosed by these portioning members with the liquid materialsconstituting the different thin films. In the context of a pixelatedOLED device, banks may be provided to partition off the various pixels.

The use of banks is described in EP 0880303. In EP 0880303, it is statedthat in order to realize a full colour display device, it is necessaryto arrange organic luminescent layers that emit any one of red, greenand blue for the respective pixels. It is further stated that a problemwith this is that it is difficult to carry out patterning with highprecision. As such, EP 0880303 provides banks to fill the spaces betweenthe pixel electrodes to prevent mixing of colours of the luminescentmaterials.

EP 0989778 is also concerned with thin film formation technology thatuses banks. The method aims to overcome problems with existing banktechnology and involves subjecting the banks to a surface treatmentunder conditions such that the degree of non-affinity exhibited by thebanks for the liquid thin film material is modified by deposition ofchemical groups such as CF groups on the surface of the banks. Reducedpressure plasma treatments and atmospheric pressure plasma treatmentsare mentioned. Further, a combination of oxygen plasma treatment andfluorine-based gas plasma treatment is mentioned. The method does notuse a stamp.

It will be appreciated that the use of banks complicates the process ofmanufacturing a device and thus makes it less time and cost effective.

Therefore, it is an object of the present invention to provide asimplified but effective method for patterning a device layer.

Accordingly, in a first aspect of the present invention, there isprovided a method for patterning a device layer using a patterned stampcomprising steps of:

(1) providing a substrate;

(2) bringing the patterned stamp into contact with the substrate

(3) removing the patterned stamp;

characterised in that step (2) is carried out so that the surface energyof the substrate is modified in accordance with the pattern; and thatthe method further comprises a step;

(4) depositing a solution of a device layer on the substrate after thepatterned stamp has been removed, whereby the surface energy of thesubstrate determines the deposition pattern of the device layer.

The method provides a convenient way to build (polymer) microstructuresfor application in (polymer) microelectronics device using methods suchas spin coating or dip coating. Such microstructures may be, forinstance, passively addressed (polymer) light emitting diodes (LEDs)with pixels in micro feature size.

It will be appreciated from the above that, in step (2) of the methodaccording to the first aspect of the present invention, bulk material isnot transferred either from or to the surface of the patterned stamp.This has a clear advantage over known soft lithography methods that usea patterned stamp and where bulk material is transferred from or to thepatterned stamp in the soft lithography method. Namely, in the presentmethod, the patterned stamp will not be contaminated during use. Thus,the patterned stamp can be used again and, more specifically, can beused again without subjecting it to costly and yet somewhat stillunreliable cleaning methods. A further advantage is that the surface ofthe substrate also is not contaminated during the method.

In contrast with some soft lithographic methods, it will be understoodalso that the patterned stamp per se is brought into contact with thesubstrate in the method according to the first aspect of the presentinvention. In most soft lithography methods, the stamp is not broughtinto direct contact with the substrate. Instead, a layer of device layermaterial always is interposed between the stamp and the substrate. Inthe present invention the stamp is brought into direct contact with thesubstrate with no intervening layer of material between the stamp andthe substrate and with no bulk transfer of material between the stampand the substrate. As compared with some soft lithography methods, itwill be appreciated readily that any problems of incompatibility betweenthe stamp material and device layer solvent are obviated in the presentmethod because the device layer is deposited after the patterned stamphas been removed.

The key to the present method is effective modification of the surfaceenergy of portions of the surface of the substrate. It will beappreciated from the above that soft lithography methods do not involveat all modification of surface energy of the substrate itself.

Further, it will be appreciated that no banks are needed in the methodaccording to the first aspect of the present invention. This is becausethe deposited device layer is confined to portions of the surface of thesubstrate by virtue of the difference in surface energy between theseportions and the remainder of the surface of the substrate. The abilityto omit the use of banks in the method according to the first aspect ofthe present invention greatly simplifies the method and, thus, makes itmore time and cost effective. The present invention provides analternative and much more simple solution to at least some of theproblems of previously known methods.

For the purposes of the present invention, the term “patterned stamp”may be taken to mean a stamp having one or more protruding elements suchthat when the patterned stamp is brought into contact with the substratein step (2), the one or more protruding elements are in contact with thesurface of the substrate and one or more indentations (between the oneor more protruding elements) will not be in contact with the surface ofthe substrate.

For the purposes of the present invention, the term “device layer” maybe taken to encompass any layer of material suitable for inclusion in anelectrical, mechanical or electromechanical device. As such, layers ofbank material are intended to be encompassed by this term.

In the present invention, “surface energy” is measurable by contactangle measurements. Generally, contact angles are measured on modelsurfaces.

In the present invention, preferably, the patterned stamp is a patternedelastomer. As such, any reference to a patterned stamp in the context ofthe present invention preferably is a patterned elastomer.

Preferably, in step (2), the patterned stamp is brought into conformalcontact with the surface of the substrate.

It is preferable in the present method that the morphology and/ortopography of the surface of the substrate is unchanged, particularlysubstantially or completely unchanged, after the patterned stamp hasbeen brought into conformal contact with the substrate in step (2) Thisis measurable by atomic force microscope (AFM) measurements.

Generally, step (2) is carried out under conditions and for a sufficienttime so that the surface energy of the substrate is modified inaccordance with the pattern. In this regard, step (2) is carried outunder conditions and for a sufficient time so that the surface energy ofeither (i) any portion of the surface of the substrate that is incontact with the patterned stamp or (ii) any portion of the surface ofthe substrate that is not in contact with the patterned stamp ismodified.

In step (2), the surface energy of the portion of the surface of thesubstrate that is in contact with the patterned stamp may be increasedor decreased. Alternatively, the surface energy of the portion of thesurface of the substrate that is not in contact with the patterned stampmay be increased or decreased.

On the substrate, after deposition of the device layer in step (4), thedevice layer is either (i) only on portions of the surface of thesubstrate that were in contact with the patterned stamp or (ii) only onportions of the surface of the substrate that were not in contact withthe patterned stamp.

It will be appreciated that to a large extent it is the difference insurface energy between portions of the surface of the substrate thatwere in contact with the patterned stamp and the remainder of thesurface of the substrate (which difference may be positive or negative)that will determine whether, after deposition, the device layer iseither only on portions of the surface of the substrate that were incontact with the patterned stamp or only on portions of the surface ofthe substrate that were not in contact with the patterned stamp.

Preferably, the device layer comprises an organic material. In thisregard, the present method is particularly advantageous when the devicelayer comprises an organic polymer. This is because of the difficultiesincurred with previously known methods when the device layer to bepatterned comprises a polymer, as discussed above. Conjugated polymerssolvated in a non-polar organic liquid selectively wets and spreads overan area with higher surface energy, but dewets and retracts from thearea with lower surface energy. The polymer solution is confined to thehigh surface energy area, and finally deposits by evaporation of thesolvent, and eventually generates a pattern on the surface. Wetting anddewetting properties of the solution are dependent on the properties ofthe solvent per se. As such, a non-polymeric material dissolved in aparticular solvent would behave similarly to a polymeric materialdissolved in the same solvent, having regard to wetting and dewettingproperties.

Particularly where the device layer is a part of an OLED or plastictransistor (although not so limited), the polymer preferably iselectrically conductive or semi conductive, more preferably conductive.Also preferably, the polymer is at least partially, substantially, oreven fully conjugated. Also preferably, the device layer is soluble in asolvent selected from the group consisting of xylene, ortho-xylene,toluene, benzene, mesitylene, chloroform, dichloromethane or mixturesthereof.

A solution of the device layer is deposited on the substrate in step(4). As such, deposition technique and droplet size also may be selectedso as to optimise the effect of the device layer being deposited eitheronly on portions of the surface of the substrate that were in contactwith the patterned stamp or only on portions of the surface of thesubstrate that were not in contact with the patterned stamp.

Suitable deposition techniques include spin coating, inkjet printing,dip coating and screen printing. Spin coating and inkjet printing arepreferred and inkjet printing is most preferred. In each of thesetechniques, the device layer may be deposited over the whole of thesurface of the substrate. However, after deposition, the device layerwill be either only on portions of the surface of the substrate thatwere in contact with the patterned stamp or only on portions of thesurface of the substrate that were not in contact with the patternedstamp. This is because of the difference in surface energy between theseportions and the remainder of the surface of the substrate. Thedifference in surface energy will cause the device layer material toflow either only to portions of the surface of the substrate that werein contact with the patterned stamp or only to portions of the surfaceof the substrate that were not in contact with the patterned stamp.

The final pattern, controlled by surface free energy, duplicates thestamp pattern either positively or negatively.

The polarity of any solvent may be selected so as to enhance the effectof the device layer being deposited either only on portions of thesurface of the substrate that were in contact with the patterned stampor only on portions of the surface of the substrate that were not incontact with the patterned stamp. In some cases, it may be preferablefor the solvent to be significantly non-polar. Generally, light-emittingpolymers are deposited from non-polar solvents such as xylene. PEDOT andpolyaniline generally are deposited from polar solvents such as water.

Preferably, the solvent is an organic solvent and, more preferably, isselected from the group consisting of xylene, ortho-xylene,trimethylbenzene, toluene, benzene, mesitylene, chloroform,dichloromethane and mixtures thereof.

The environment in which depositing in step (4) occurs can be optimisedin order to optimise the effect of the device layer being depositedeither only on portions of the surface of the substrate that were incontact with the patterned stamp or only on portions of the surface ofthe substrate that were not in contact with the patterned stamp.Temperature, atmospheric humidity and atmospheric pressure all should beconsidered.

As stated above, the patterned stamp must be brought into contact withthe substrate. This may be achieved simply by placing and leaving thepatterned stamp on the surface of the substrate by any suitable means.

The thickness of the deposited device layer also may affect theeffectiveness of the present method. It is usual that the thickness ofthe deposited device layer is up to 2000 Å. Preferably, an electrodedevice layer may have a thickness in the range 1000 to 2000 Å, morepreferably about 1500 Å. Other device layers such as an emissive layerin an OLED preferably have a thickness of up to 1000 Å.

It has been found that faithful reproduction of the pattern on thepatterned stamp on the surface of the substrate is achievable. Inparticular, faithful reproduction has been achieved where the featuresize of the pattern can be varied from 20 microns to 500 microns with aresolution of a few microns. Feature sizes in this range are suitablefor forming a device layer in an OLED.

Modification of the surface energy in step (2) of the present method maybe a transient effect. As such, step (4) must be carried out, in thepresent method while the effect still is strong enough to result in apatterned device layer. Accordingly, it is preferred that step (4) iscarried out directly after step (3), more preferably immediately after.

In a first embodiment of the present method, in step (2), the surfaceenergy of any portion of the substrate that is in contact with thepatterned stamp is modified. This modification may be, for example, bytransfer of chemical groups (i) from the surface of the patterned stampto any portion of the surface of the substrate that is in contact withthe patterned stamp and/or (ii) from any portion of the surface of thesubstrate that is in contact with the patterned stamp to the surface ofthe patterned stamp. Also, this modification may be by rearrangement ofchemical groups on the surface of any portion of the surface of thesubstrate that is in contact with the surface of the patterned stamp.Infrared reflection-absorption spectroscopy (IRAS), can be carried outin order to chemically characterize the modified surface of thesubstrate and also the surface of the patterned stamp.

In this embodiment, the modification of the surface energy by contactwith the patterned stamp is the most crucial step during the patterningprocedure; the interfacial surface free energy between device layer(usually a polymer solution) and the patterned stamp is the essentialdriving force controlling the patterning.

According to the first embodiment of the first aspect of the presentinvention, the patterned stamp has a function to modify the surfaceenergy of the substrate, typically a film formed from aqueous solution.No additional surface energy modifying process is needed. As thepatterned stamp is applied on a substrate surface for a time period itcan turn some surfaces from high surface energy to low surface energyand can turn other surface from low surface energy to high surfaceenergy. The change in surface energy is attributed to the interactionbetween the stamp surface (usually elastomer molecules) and thesubstrate surface. The formation of either a positive pattern or anegative pattern can be understood by the requirement of minimization offree energy of whole system. Surface energy directs liquid to the highsurface energy area where contact angle is lower. Liquid easily wets andspreads over the area and finally deposits on the hydrophobic area afterthe solvent evaporates. A pattern generated in a positive or a negativemanner with respect to the patterned stamp depends on modificationeffect. A positive pattern can be formed when the patterned stampmodifies a surface from low surface energy to high surface energy. Anegative pattern can be generated when the patterned stamp modifies asurface from high surface energy to low surface energy. Patterning ofpolymer on a modified PEDOT-PSS surface by spin coating, for example,demonstrates the very strong adhesive force between polymer solution andhigh surface energy area. The larger difference in surface energy or incontact angle is indeed a crucial rule for the patterning procedure.

It will be appreciated that the stamp material may be selected so as tooptimise the surface energy modifying effect in the first embodiment ofthe present method. In this embodiment, it is preferred that the stampis an elastomer and a particularly preferred elastomer ispoly(dimethylsiloxane)(PDMS) and equivalents thereof. PDMS is solventresistant and is soft and flexible with a low surface energy such thatit may easily be removed from the substrate. Further, it has been foundthat particularly good resolution can be obtained using PDMS as thepatterned elastomer. Specifically, resolution has been found to improvethreefold over previous photolithography methods for patterning a devicelayer.

Further, it will be appreciated that the substrate material may beselected so as to optimise the surface energy modifying effect in thefirst embodiment of the present method.

To this end, in the first embodiment of the present method, it ispreferred that the substrate is polar. Specifically, it is preferredthat the substrate material includes charged groups, more preferablycharged groups such as sulfate, carboxylate etc.

The present method is particularly advantageous when the substratecomprises a polymer, preferably an electrically conductive orsemiconductive polymer. More preferably, the polymer is at leastpartially, substantially, or even fully conjugated.

The polymer advantageously is a charge transporting polymer or a chargeinjecting polymer, optionally with a negatively or positively chargedopant. The charged dopant may be used to enhance the patterning effect.More advantageously, the polymer is selected from the group consistingof poly (3,4-ethylenedioxythiophene) (PEDOT), poly(3,4-ethylenedioxy-thiophene)-poly(styrenesulfonate) (PEDOT-PSS),polyaniline with acid dopant and polyaniline-PSS. It is most preferredthat the substrate is PEDOT on a layer of ITO.

In this embodiment, it is preferred that the patterned stamp is broughtinto contact with the surface of the substrate at room temperature andat ambient humidity. In this regard, the temperature should be such thatthe thermal energy of the substrate is not great enough to overcome anysurface modification due to contact with the patterned stamp.

Further, in this embodiment, it will be appreciated that themodification of the surface energy is due to inherent properties of thepatterned stamp and substrate material. It will be a time dependenteffect. Thus, it is preferred that the patterned stamp is in contactwith the substrate for a period of time sufficient to allow this effectto proceed to completion/its maximum. Typically, this period will belonger than one day or more typically longer than two days and mosttypically up to several days.

In a second embodiment of the present method, in step (2) the surfaceenergy of any portion of the substrate that is not in contact with thepatterned stamp is modified. In this embodiment, the patterned stamp isused as a mask in step (2) and step (2) includes subjecting any portionof the surface of the substrate that is not in contact with thepatterned stamp to a surface energy modifying process. Any suitablesurface energy modifying process known in the art may be used so long asit produces the desired effect. Suitable surface energy modifyingprocesses include exposure to UV radiation, plasma treatment.

The second embodiment of the present method will be particularly usefulwhen the substrate material is not responsive to surface modificationmerely by bringing a patterned stamp into contact with the substrate. Anotable substrate material in this regard is indium tin oxide, a commonmaterial used for the anode in OLEDs.

In the second embodiment, O₂/CF₄ plasma treatment may be carried out ina RF barrel etcher of dimensions about 300 mm diameter, about 450 mmdepth, with a gas mixture of about 0.5-2% CF₄ in oxygen, at a pressureof about 1.5 Torr and a power of about 400 W. The treatment suitably iscarried out for about 10-30 s. In the case of exposure to UV radiation,the UV light source may be an Ushio UER 200-172 lamp providing 7 mW/cm²at a wavelength of 172 nm. Suitably, the UV light source may bepositioned about 1.1 mm from the substrate. The treatment suitably iscarried out for about 15 s.

In the second embodiment, it is preferred that the stamp is an elastomerand a particularly preferred elastomer is poly(dimethylsiloxane)(PDMS)and equivalents thereof.

In a second aspect according to the present invention, there is provideda method for making an electrical, mechanical, or electromechanicaldevice including a method according to the first aspect of the presentinvention.

In this second aspect of the present invention, the substrate providedin step (1) typically will be supported by one or more further devicelayers, at least one of which may be a patterned device layer. Also,typically, the method according to the second aspect of the presentinvention will include a further step (5) of depositing on the devicelayer deposited in step (4) one or more further device layers.

Preferably, the method according to the second aspect is a method formanufacturing an optoelectronic device, more preferably, theoptoelectronic device is selected from an OLED, specifically a pixelatedOLED, a transistor, a solar cell, a photodiode, a diffraction grating, amicrocircuit, specifically a printable microcircuit, and a microfluidicdevice.

An important pixelated OLED device is a flat panel display (FDP). TheFPD may be used in products including cellular phones, cellular smartphones, personal organisers, pagers, advertising panels, touch screendisplays, teleconferencing equipment, virtual reality products, anddisplay kiosks.

The method according to the second aspect of the present inventionprovides a convenient way to, build polymer microstructure forapplication in polymer microelectronics device, like passively addressedpolymer light emitting diodes, (LEDs) displays, optically pumpedmicro-patterned polymer micro cavities and field effect transistors(FETs).

A method for manufacturing a monochrome OLED device is describedgenerally below:

-   -   Provide a transparent, typically glass, substrate    -   Provide an anode layer, typically ITO, on the transparent        substrate where the anode is patterned in parallel lines. This        may be achieved using photolithographic and etching techniques    -   Deposit a layer of polymer, for example a semiconductive polymer        such as a hole transport polymer (e.g. PEDOT-PSS), on the anode        layer by a suitable deposition technique such as spin coating    -   Bring a patterned stamp into contact with the semiconductive        polymer layer, the pattern of the patterned stamp being such        that the surface of the semiconductive polymer layer is modified        in lines orthogonal to the parallel anode lines    -   Spin coat or inkjet print a device layer, such as a        light-emissive polymer, on the semiconductive polymer layer.        After deposition, the polymer will be in parallel lines        (orthogonal to the ITO parallel lines) in accordance with the        pattern of the patterned stamp    -   Deposit cathode material in parallel lines that also are        orthogonal to the ITO parallel lines. This may be carried out by        a masking technique.

In the above general method, it will be appreciated that a patternedstamp according to the present invention also may be used to pattern theanode and the cathode, provided that the anode or cathode can bedeposited from solution. Also, it will be appreciated that furtherdevice layers, other than those explicitly referred to, may be provided.The further device layers may be selected from hole transport layers andelectron transport layers and also may be patterned using a patternedstamp according to the present invention.

The above method may be modified for the preparation of a colour device.Instead of the patterned stamp being patterned so that parallel lines ofspin-coated polymer are formed, the patterned stamp should be patternedso that the surface energy of the polymer is modified in accordance witha well or pixel structure. Red, Green and Blue light-emitting polymersthen can be inkjet printed into the wells as required.

Cathode then can be deposited in accordance with the monochrome deviceabove.

The above descriptions of monochrome and colour device structures areintended to be examples only. Those skilled in the art will readilyappreciate modifications in accordance with this invention that could bemade to these device structures.

According to a fourth aspect of the present invention, an electrical,mechanical or electromechanical device is provided as defined above inrelation to the second aspect of the present invention. Suitably, thedevice may be obtained by the method according to the second aspect ofthe present invention. The device contains at least a patterned devicelayer supported on a substrate.

In devices according to the fourth aspect of the present invention, thesurface of the substrate that is in contact with the patterned devicelayer is substantially flat, without relief features. This may becontrasted with some prior art devices where “banks” are used to createrelief features on the surface of the substrate.

Regions of patterned device layer in devices according to the fourthaspect of the present invention are not separated by physical means.

Preferably, the patterned device layer comprises a polymer.

Also preferably, the substrate is charged and/or comprises a polymer.

One or more further device layers may be supported on the patterneddevice layer and/or the substrate may be supported on one or morefurther device layers, as required. One or more of the further devicelayers may be patterned, as required.

Preferably, the electrical, mechanical or electromechanical device is anoptoelectronic device. More preferably, the optoelectronic device isselected from the group consisting of an OLED, a transistor, adiffraction grating, a microcircuit and a microfluidic device. Even morepreferably, the optoelectronic device is an OLED.

The present invention now will be described in more detail withreference to the accompanying drawings in which:

FIG. 1 shows a cross section of a typical OLED device according to thepresent invention;

FIG. 2 shows a typical OLED device known in the art using “banks”;

FIG. 3 shows the principle of surface energy controlled patterningaccording to the first embodiment of the first aspect of the presentinvention.

FIGS. 1 and 2 clearly show the differences between a device according tothe present invention and devices known in the art. In FIGS. 1 and 2,reference numeral 1 refers to a substrate; reference numeral 2 refers toan anode layer, usually ITO, that is patterned to form parallel linesrunning in the direction A-A′. Reference numeral 3 indicates a holetransport layer, for example PEDOT. Reference numeral 4 indicates apolymer device layer. Layer 4′ is deposited by the method according tothe first aspect of the present invention to form parallel linesorthogonal to the anode lines. Layer 4″ is deposited between the banks6. Reference numeral 5 indicates a cathode that is deposited over thepolymer layer for example by shadow masking.

The principle of surface energy controlled patterning of polymers usingPDMS stamp is illustrated in FIG. 3. FIG. 3 shows a film of material 32such as PEDOT-PSS on a substrate 31 which is typically glass. PDMS stamp33 is brought into contact with the surface of material 32. Removal ofthe PDMS stamp leaves areas of material 32 with modified surfaceproperties indicated by 34. A layer of conjugated polymer is thendeposited upon the modified surface of material 32, deposition may beby, for example, spin coating or dip coating. Depending on the nature ofthe film of material 32 and the nature of the conjugated polymer whichis deposited. Deposition of the conjugated polymer may result in apositive patterned area of conjugated polymer 35 or negative patternedarea of conjugated polymer 36.

Following is the description and characteristic measurement of oneprocessing procedure according to the first embodiment of the methodaccording to the first aspect of the present invention.

Preparation of poly (dimethylsiloxane) PDMS stamp:Two parts of Sylgard184 silicone elastomer (Dow Corning Corp.), base and curing agent withratio of 10:1 in mass, are mixed together in a container. This isfollowed by degassing of the mixture in a vacuum chamber until airbubbles no longer rise to the top. To avoid air inclusion, it isnecessary to slowly pour the mixture on a template that has SU 8 (MicroChem Corp.) photoresist patterns generated by normal photolithography,on a silicon wafer. Curing of the elastomer is done at 140° C. in anoven for 15 minutes. A PDMS stamp is ready to be used for surfacemodification.

Modification of surface: To modify a film surface, the PDMS stamp isbrought in conformal contact with the film surfaces. Samples are kept atroom temperature and with ambient humidity. The contacting time ofmodification is 2 days.

Poly (3,4-ethylenedioxythiophene)-poly (styrenesulfonate) (PEDOT-PSS)and poly (sodium 4-styrenesulfonate) sodium salt (NaPSS) films areformed by spin coating from their aqueous solution. Standard PEDOT-PSSsolution is a water dispersion (purchased from Bayer), 1.3%concentration in mass; NaPSS solution is prepared by dissolvingcompounds NaPPS (Aldrich), into deionized water with concentration of 1%in mass; The spinning speed to deposit above films is 3000 rpm and 2000rpm, giving ˜700 Å thickness of these two films, respectively. Theconjugated polymer film is formed on glass substrates with spin coatingfrom organic solutions of the polymer, in which xylene, or chloroform isused as solvent. The concentration of the polymer solution is 1.4% inmass in general. Modifying these surfaces is done by bringing a flat orstructured stamp in conformal contact with surface for time periods ofup to 2 days.

Contact angle is determined as the stamp is removed from the modifiedsurface. Contact angle measurement: Contact angle measurement isperformed on a contact angle goniometer (Model 100-00) at roomtemperature (T-21°) and ambient humidity. By using the Model 100-10micro syringe attachment, a pendant drop above measuring surface for 1mm, is dispensed onto the surface. A non-polar organic solvent,N-hexadecane is used as test liquid.

In order to determine the optimal modification time for a perfectpattern, the relation between contact angles and modification time areinvestigated.

Morphology measurement with atomic force microscope: The topography ofmodified film surfaces are measured by an atomic force microscope (AFM)(Nanoscope III, Digital Instruments). PEDOT-PSS and NaPSS film aredeposited on a glass substrate by spin coating. The surfaces of thesefilms are modified by patterned PDMS stamp, and the modification time istwo days. After the stamp is removed, the topography is investigated byAFM. In this study, the stamps applied on the surfaces have patternpitch/period of 22 μm, barrier rib, barrier gap are 14 μm and μm inwidth, respectively. It is not possible to distinguish any differencebetween the modified and unmodified surface areas by the naked eye orthrough an optical microscope.

Time Profile of Modification: The contact angle of PEDOT-PSS beforemodification is around 36° and that for NaPSS is about 9°, respectively.This indicates that the surface energy of PEDOT-PSS before modificationby a PDMS stamp is lower than that of NaPSS. Liquids wet and spread onNaPSS film more easily than on the PEDOT-PSS film before surfacemodification takes place.

The contact angle of hexadecane on PEDOT-PSS or NaPSS is dramaticallychanged after surface modification by PDMS stamp. This change is timedependent. The contact angle on PEDOT-PSS decreases linearly from 22° to12_20 with modification time from 25 min. to 100 hrs. For NaPSS, contactangles increase linearly from 270 to 330 with logarithmic modificationtime from 25 min. to 100 hrs. During the first four hours the contactangles rapidly change, but then slow down until they approach a steadyvalue.

The changes in surface energy by modification with PDMS stamp aresignificant. After modification, the surface energy of PEDOT-PSS isreduced, but that of NaPSS is increased. Consequently, polymer solutionwith organic nonpolar solvent wets and spreads and finally covers amodified PEDOT-PSS film surface. On the modified NaPSS film surface, theliquid wets the unchanged areas. The difference in contact angle betweenmodified and unmodified film is 25° for PEDOT-PSS film, and slightlysmaller for NaPSS case, 23°. We suggest that this surface energydifference on a surface will influence the confinement of liquids. Thepolymer solution selectively wets and spreads only on the area withhigher surface energy, controlled by surface energy difference forminimization of the surface energy of the entire system. Spin coating ordip coating polymer solution on such a modified surface can generate apositive or negative pattern depending on the character of surfaceenergy after the modification. A positive pattern might be generated asthe surface energy of the film increases after modification; when thesurface energy is increased by modification, the confinement generates anegative pattern. A conjugated polymer can be patterned on the modifiedPEDOT-PSS film surface by dip coating or spin coating from solution.

The surface morphology has been imaged with AFM in tapping mode. Bothheight and phase images of PEDOT-PSS and NaPSS surface show aperiodicity that is consistent with that of stamp with a bulge linealong the boundary of the area where the surface has been contacted withstamp. The height of this bulge line on NaPSS surface is determined tobe 30 nm, while the height on the PEDOT-PSS surface along the boundaryof stamped areas is very small.

The variation of height between the stamped area and not stamped areacan be negligible except for the bulge line at the boundary of thestamped area, indicating that no bulk material is transferred from thestamp to the surface during the process. The bulge may be caused by alarger interaction force between the patterned elastomer and the surfaceof substrate due to the higher pressure existing at the edge of thepatterned elastomer contact area. It cannot be excluded that thesebulges help in confining the polymer solution to certain areas in laterprocessing steps. However, the AFM images tell us that surface energyrather than topography directs the polymer solution to the desiredareas.

Infrared reflection-absorption spectra (IRAS) measurements: IRAS is usedto chemically characterize the modified surface.

Substrates are prepared by thermally evaporating Cr (4.4 nm) and Au (150nm) on cleaned silicon wafers at vacuum lever of 2*10⁻⁷ Torr. Therefollows a standard cleaning process, substrates are boiled in TLisolution (5:1:1H₂O, NH₃.H₂O and H₂O₂ in volume) at 90° for 15 min.Subsequently a PEDOT-PSS and a NaPSS layer is formed by spin coating onseparate substrates with speed 5000 and 4000 rpm, respectively, theirthickness are less than 40 nm.

The surface modification is done by bringing two flat stamps inconformal contact with PEDOT-PSS and NaPSS surface for 2 days. Afterremoving stamps the modified PEDOT-PSS and NaPSS surfaces are obtained.A Bruker IFS 113v FTIR spectrometer with a grazing angle accessoryaligned at 85°-incidence angle is employed. In order to analyze thechanges in chemical compounds on the surface modified by PDMS stamp, theIRAS of pure Au, PEDOT-PSS, NaPSS and modified PEDOT-PSS and NaPSSsurface are measured.

Except CO₂ and H₂O vibration bands, all vibration peaks observed arecorresponding to —CH₃, and —C—Si—, which definitely originate from PDMSmolecule but not from PEDOT-PSS and NaPSS molecule, revealing thatmaterials from PDMS stamp has transferred onto PEDOT-PSS and NaPSSsurface during PDMS stamp modification. However this is evidence of thetransfer of chemical groups from the stamp rather than evidence oftransfer of bulk material from the stamp.

Without wishing to be bound by theory it is considered that during PDMSstamp surface modification the polar group —CH₃ tails in PDMS, which arehydrophobic and with higher surface energy, prefer to link with thePEDOT-PSS surface which is more hydrophilic and has a higher surfaceenergy before modification (contact angle of n-hexadecane on the surfacewithout surface modification θ₁=36°). This leads —OSi— bonds stand onthe top surface when the PDMS stamp is removed from the substrate,resulting in the PEDOT-PSS surface being modified from high to lowsurface energy, and contact angle on modified surface reducing to θ₂=90°Similarly, during modification of NaPSS by PDMS stamp the —C—Si— groupof the PDMS molecule prefers to link to the NaPSS surface due to the lowsurface energy of the NaPSS film and the —C—Si— group being morehydrophilic, resulting in —CH₃ tails having more freedom of movement andfacing upwards on the NaPSS surface. This is considered to be the reasonwhy PDMS modification turns NaPSS surface energy from low to high,therefore increasing the contact angle from θ₃10° to θ₄=33°.

Surface energy controlled patterning of polymer: The deposition andpatterning of conjugated polymer on the modified PEDOT-PSS and NaPSSsurface can be achieved by dip coating or spin coating from the organicsolution. Photographs of polymer patterns deposited on these modifiedsurfaces are taken by a reflective or an inverted transmissionmicroscope equipped with a digital camera (Sanyo, colour camera), underwhite light or under UV irradiation, The photoluminescence emission fromconjugated polymer gives a high contrast image.

A patterned film is prepared by dip coating or spin-coating asemiconducting conjugated polymer xylene solution on a PEDOT-PSS surfacemodified by a stamp. The pattern positively copies stamp structure,which is consistent with the contact angle measurements. The patterndeposited can be in the form of for example squares, rectangles or thicklines, according to the stamp structure. A line pattern is deposited bydip coating on modified PEDOT-PSS surface. A photograph taken undernormal illumination reveals that the patterned line is 40 μm in width,separated by 5 μm gap between lines. A square-shape pattern is generatedby spin coating a light emitting conjugated polymer (a blend of apolyfluorene-benzothiadiazole copolymer and a polyfluorene-triarylaminecopolymer) from xylene solution on a modified PEDOT-PSS surface.Photographs may be taken under the illumination of UV light (365 nm).The side of the squares can be in range from 50 μm to 250 μm long,spacing with 25 μm to 200 μm.

A conjugated polymer was deposited by dip coating the polymer solutionon a modified NaPPS surface. The NaPPS surface was modified by contactwith a PDMS stamp having a relief pattern of rectangles, the side ofrectangleses being 100 μm and 200 μm, with the spacing between adjacentrectangleses being 200 μm. The pattern generated on the modified NaPSSsurface is the negative of the pattern of the stamp, meaning that thepolymer solution finally settles on areas that have not been in contactwith the PDMS stamp. These areas having higher surface energy comparedwith that of areas brought into contact with the stamp. This result isopposite to the results of patterning of the conjugated polymer onto amodified PEDOT-PSS surface.

1. A method for patterning a device layer using a patterned stamp,comprising the steps of: (a) providing a substrate; (b) bringing thepatterned stamp into contact with the substrate; (e) removing thepatterned stamp from the substrate; (d) depositing a solution of adevice layer on the substrate after the patterned stamp has beenremoved; whereby the surface energy of the substrate determines thedeposition pattern of the device layer wherein step (b) is carried outso that the surface energy of the substrate is modified in accordancewith the pattern.
 2. (canceled)
 3. (canceled)
 4. A method according toclaim 1, wherein the topography of the surface of the substrate isunchanged after the patterned stamp has been brought into contact withthe substrate.
 5. A method according to claim 1 comprising depositingthe device layer is by spin coating or inkjet printing.
 6. A methodaccording to claim 1, wherein the solvent is selected from the groupconsisting of xylene, ortho-xylene, toluene, benzene, mesitylene,chloroform, dichloromethane, and mixtures thereof.
 7. (canceled)
 8. Amethod according to claim 1, wherein in step (b) the surface energy instep (b) of any portion of the surface of the substrate that is incontact with the pattern stamp is modified.
 9. A method according toclaim 8, wherein the substrate comprises a polymer.
 10. A methodaccording to claim 9, wherein the polymer is poly(3,4-ethylenedioxythiophene) or polyaniline.
 11. A method according toclaim 8 to 10, wherein the substrate is charged.
 12. (canceled)
 13. Amethod according to any one of claims 1 to 7, wherein the patternedstamp is used as a mask in step (b) and step (b) includes subjecting anyportion of the surface of the substrate that is not in contact with thepatterned stamp to a surface energy modifying process.
 14. A methodaccording to claim 13, wherein the surface energy modifying processincludes a step of exposing any portion of the surface of the substratethat is not in contact with the patterned stamp to UV radiation. 15.-23.(canceled)